I've been looking into less lethal firearms like the Umarex TR50 or HDX 68 because I can get them more quickly (don't need training/licensing) and if I end up having to use them it's less likely to get police or courts involved, whom I do not trust to be sympathetic, and you shouldn't either. In addition to versions which are colored bright orange to denote low lethality, there are black versions that look like guns at a glance, which may be enough deterrent/intimidation factor to make a brownshirt pause for a moment, during which time you fire pepperballs, which should disable them long enough for you to get away. The TR50 revolver can be loaded with a mix of those and hard pellets which will hurt like hell if aimed properly, and the HDX 68 has a sharp butt which can be jabbed in close quarters if needed.

But--going back to my earlier point--none of this does any good if it's the police themselves or the military coming for you, nor will a conventional weapon help that much in that situation, frankly.